Despite considerable advances toward understanding the molecular basis of calcium and phosphorus transfer across the intestine and other epithelial membranes, much is yet to be revealed. This also pertains to the molecular basis of vitamin D action. The proposed investigations represent a continuing effort to uncover new aspects of the problem and to aid in defining the mechanisms involved, which should find relevance to specific human and animal disease states. Detailed investigations on the properties (including both amino acid sequence and x-ray crystallographic studies), cellular and subcellular localization, distribution and function of the vitamin D-induced, calcium-binding protein (CaBP) and other vitamin D-dependent molecules will continue. Emphasis during this period will be devoted to defining the integral membrane proteins potentially involved in intestinal calcium and phosphate transport. Included will be a detailed investigation of alkaline phosphatase-CaATPase complex the brush border and basal-lateral membrane. This molecule is responsive to 1,25-(OH),D3 and bears some relation to calcium transport. In addition, attempts will be made to reconstitute the calcium and phosphate transport by transferring membrane molecules to liposomes and possibly other artificial membranes. Supportive evidence for a shunt path for calcium across the intestine will be sought. Detailed investigations on the physiological and molecular basis of phosphate absorption are planned. The potential applications of these findings to pertinent disease states in humans and animals will be continually surveyed.